Investigation of the Freezing Phenomenon in Vials Using an Infrared Camera

The freezing phenomenon has a dramatic impact on the quality of freeze-dried products. Several freezing models applied to solutions in vials have been proposed to predict the resulting product morphology and describe heat transfer mechanisms. However, there is a lack of detailed ex-perimental observations of the freezing phenomenon in vials in the literature. Thus, the present work offers new experimental observations of the freezing phenomenon in vials by infrared (IR) thermography. IR imaging allowed each vial's whole axial temperature profile to be collected during freezing, which offersproviding significant insights into the process. Spontaneous nucle-ation and vacuum-induced surface freezing (VISF), as a controlled nucleation technique, are in-vestigated. Batches having vials in direct contact with the shelf (exchanging heat mainly through conduction) as well as suspended (exchanging heat mainly through natural convection and radi-ation) were tested. The study used three solutions: sucrose 5%, mannitol 5%, and dextran 10%. SEM images coupled with an automated image segmentation technique were also performed to ex-amine possible correlations between the freezing observations and the resulting pore size dis-tributions. IR thermography was found to be a promising tool for experimentally predicting the resulting product morphology in-line.